1. Field of the Invention
The present invent ion relates to ohmic electrode materials and semiconductor ceramics elements made thereof and, in particular, to ohmic electrode materials for semiconductor ceramics having an ohmic contact and semiconductor ceramics elements made thereof such as positive temperature coefficient thermistors, varistors and resistors.
2. Description of the Prior Art
As electrode materials of various semiconductor ceramics such as barium titanate system semiconductor ceramics, zinc oxide system semiconductor ceramics, strontium titanate system semiconductor ceramics, tin oxide system semiconductor ceramics, iron oxide system semiconductor ceramics, titanium oxide system semiconductor ceramics and nickel oxide system semiconductor ceramics are used electrode materials having an ohmic contact.
As such electrode materials having an ohmic contact are known, among others, In-Ga alloy, electroless deposition of nickel, ohmic silver paste and aluminum paste.
Of these electrode materials, one comprising aluminum paste is applied to the surface of a semiconductor ceramics by, for example, printing and then baked at 600.degree.-800.degree. C. for electrodes to be formed thereby. This aluminum electrode is lowest in specific resistance of all base metals, also being lowest in manufacturing cost and thus presenting the cheapest base metal electrode material.
The aluminum electrode with its short life in a moist atmosphere, however, has a problem of having its resistance increasing with increasing ambient humidity, and it is not yet in practical use.